Galvanic cell having improved construction

ABSTRACT

A GALVANIC CELL IS DISCLOSED. THE CELL COMPRISES A METAL CAN HAVING A WALL WITH AN INNER SURFACE, A TOP, AND A BOTTOM, DEPOLARIZING MIX PARTIALLY FILLING SAID CAN SUCH THAT THERE IS A SPACE BETWEEN THE TOP OF THE MIX AND THE TOP OF THE CAN, A CURRENT COLLECTING ROD IN SAID DEPOLARIZING MIX IN CONTACT THEREWITH AND EXTENDING OUTWARDLY THEREFROM TO AT LEAST THE TOP OF SAID CAN, A PAPER LINER SEPARATING SAID DEPOLARIZING MIX FROM SAID CAN, AND A STRIP OF PLASTIC FILM ATTACHED TO THE TOP OF SAID PAPER LINER, THE FILM BEING SHRUNK AWAY FROM THE INNER SURFACE OF THE WALL OF THE CAN. IN THE PREPARTION OF THE CELL, THE STRIP OF PLASTIC FILM THAT IS ATTACHED TO THE TOP OF THE PAPER LINER ACTS AS A SHIELD OR APRON TO PROTECT THE CAN FROM BEING SMEARED WITH DEPOLARIZING MIX AS THE MIX IS BEING INSERTED IN THE CAN. THE PLASTIC FILM IS THEN HEAT SHRUNK AWAY FROM THE INNER SURFACE OF THE WALL OF THE CAN. THE GALVANIC CELL OF THE INVENTION HAS REDUCED TENDENCY TO LOSE MOISTURE FROM THE DEPOLARIZING MIX AND FROM THE SEPARATOR.

Juy 24 i973 v. s. ALBERTO GLVANIC CELL HAVING IMPROVED CONSTRUCTIONFiled July 21, 1971 2 Sheets-Sheet l INVENTOR VICENTE S. ALBERTO July24, i973 V. S` ALBERTO GALVANIC CELL HAVING IMPROVED CONSTRUCTION FiledJuly 21, 1971 2 Sheets-Sheet 2 @gli INVENTOR VICENTE S. ALBERTO ATTORNEYUnited States Patent O 3,748,181 GALVANIC CELL HAVING IMPROVEDCONSTRUCTION Vicente S. Alberto, Cleveland, Ohio, assigner to UmonCarbide Corporation, New York, N.Y. Filed July 21, 1971, Ser. No.164,518 Int. Cl. H01m 21 00 U.S. Cl. 136-107 7 Claims ABSTRACT F THEDISCLOSURE A galvanic cell is disclosed. The cell comprises a metal canhaving a wall with an inner surface, a top, and a bottom, depolarizingmix partially filling said can such that there is a space between thetop of the mix and the top of the can, a current collecting rod in saiddepolarizing mix in contact therewith and extending outwardly therefromto at least the top of said can, a paper liner separating saiddepolarizing mix from said can, and a strip of plastic film attached tothe top of said paper liner, the lm being shrunk away from the innersurface of the wall of the can. In the preparation of the cell, thestrip of plastic lm that is attached to the top of the paper liner actsas a shield or apron to protect the can from being smeared withdepolarizing mix as the mix is being inserted in the can. The plastic lmis then heat shrunk away from the inner surface of the wall of the can.The galvanic cell of the invention has reduced tendency to lose moisturefrom the depolarizing mix and from the separator.

The invention relates to a galvanic cell having an improvedconstruction.

In U.S. Pat. 2,962,844, Orlando et al., one method for the production ofpaper-lined galvanic cells is proposed. Referring especially to FIGS. 40through 50 of this patent, various steps in one process for producingpaper-lined cells is shown. In accordance with this prior art process, arolled up cylinder of paper is iirst inserted in a metal can. Thecylinder extends from the bottom of the can to the top. Thereafter, abottom liner in the form of a cup is inserted in the can. Thedepolarizing mix is then added to the can. The depolarizing mix lls thecan only part way. Thereafter, the top edge of the paper liner is foldeddown in order to make room for the closure disc which is to be insertedin the top of the can as a seal. 'I'he current collecting rod is theninserted in the depolarizing mix, and the closure disc is positioned inthe top of the can. The reason that the paper liner initially extendsall the way to the top of the can, even though it is subsequently foldeddown, is to act as a shield for the can while the depolarizing mix isbeing added. lf it were not for this shield, the depolarizing mix wouldsmear the can in some cases, and cause either low voltage or perforationof the can. The folding down of the upper portion of the paper liner isnot a satisfactory operation on a commercial scale. It must be donemechanically, and it is diicult to do this on a mass production basis,especially with smaller sized cans such as those being employed to makeN, A, AA, and other small sized galvanic cells. Therefore, as apractical matter, in the commercial production of small sized galvaniccells, the paper liner does not extend to the top of the can when it isiirst inserted, in order to avoid the need for folding the paper down.As a result, there is a significant percentage of cells that arerejected because the depolarizer mix smears the inside of the can.

A disadvantage that inheres in the use of paper liners, regardless ofwhether or not the upper portion is folded down, is that the paperextending above the top 0f the depolarizer mix acts as a wick to carrymoisture out of both the separator and the depolarizer mix and into theair space above the mix. Some of this moisture is 10st during venting ofthe cell, with the result that the separator and the mix have a tendencyto dry out. A dry separator is disadvantageous because it causes anincrease 1n internal resistance and lessened electrolytic Contact withthe anode. A dry mix is disadvantageous because it lowers the amount ofelectrical energy that the cell can deliver. One further problem is thatsmall amounts of oxygen from the air can enter the cell during venting.The paper liner from which moisture has been lost, and which extends upinto the air space, can provide a pathway through which oxygen candiffuse and thereby contact the inner surface of the anode. This cancause corrosion.

The present invention provides a means for substantially eliminating therisk of depolarizer mix smearing of the can during cell production, andat the same time, a means for producing a cell having less of a tendencyto lose moisture from the separator and depolarizer mix, and less of atendency to permit oxygen from the air to contact the anode, therebyimproving the shelf life of cells made in accordance with the invention.

It is an object of the present invention to provide a means for thepreparation of paper lined galvanic cells wherein fewer rejects aremade.

It is another object of the invention to provide galvanic cells having alessened tendency to lose moisture.

It is a further object of the invention to provide a galvanic cellhaving a reduced tendency to permit oxygen to contact the anode.

These and other objects and advantages of the invention will be apparentfrom the following description, taken in conjunction with the drawings,wherein:

FIG. l is a cut away elevation, partly in section, of a metal batterycan that can be employed to produce the galvanic cells of the invention;

FIG. 2 is a cut away elevation, partly in section, showing a paper linerhaving a plastic strip on the top being inserted in the battery can ofFIG. l;

FIG. 3 is a cut away elevation, partly in section, of a metal batterycan having the liner in place;

FIG. 4 is a cutaway elevation, partly in section, showing the bottom cupor Washer being inserted in the lined battery can of FIG. 3;

FIG. 5 is a side elevation, in cross section, of a lined battery can towhich the depolarizing mix has been added;

FIG. 6 is a side elevation in cross section showing`a lined battery cancontaining depolarizing mix after the current collecting rod has beeninserted in the mix;

FIGS. 7 and 8 show various stages in the heat shrinking operationwherein the strip of plastic film is heat shrunk away from the innersurface of the wall of the can;

FIG. 9 shows the cell after the plastic film has been heat shrunk awayfrom the inner surface of the wall of the can;

FIG. 10 shows a paper battery separator having a strip of plastic filmattached at the top; and

FIG. 11 is a side elevational, partly schematic view of an apparatusthat can be used for heat sealing a strip of .plastic film to a strip ofbattery separator paper.

being shrunk away from the inner surface of the wall of the can.

In FIG. a separator suitable for use in the invention is shown. Theseparator includes a generally rectangular piece of paper 21 having astrip of heat shrinkable plastic film 23 attached to the entire top edgeof said paper 21. The Width of the seam 25, or area of film/paperoverlap, is not critical. For instance, seam widths of from aboutone-sixteenth to about three-sixteenths of an inch are acceptable. Anyconventional type of battery separator paper can be employed in theinvention, including kraft paper, alpha-cellulose paper, and otherporous, pinhole free paper. The paper is usually unsized, and may becoated on at least one side With materials such as methyl cellulose toimprove the electrolytic contact with the inner surface of the Wall ofthe can.

The heat shrinkable plastic film 23 that is attached to the top of thepaper 21 can be any type of heat shrinkable plastic film that isimpervious to the depolarizing mix. Such plastic films that can be usedinclude polyethylene, polypropylene, polystyrene, polyvinyl chloride,polyvinylidene chloride/Vinyl chloride copolymer, and polyester, whichare well known in the art. 'Ihe thickness of the film willl normally befrom about one-half to about three m1 s.

The plastic tilm 23 can be attached to the paper 21 by any convenientmethod such as by heat sealing or by the use of adhesives. (If coatedpaper is used, the plastic film can be bonded to either the coated orthe uncoated side of the paper.) In FIG. ll an apparatus that canconveniently be used for heat sealing a strip of plastic to a strip ofseparator paper is shown. The apparatus includes a steel rotatable drum27, guide rollers 29 and 31, and heaters 33 and 35. In operation, theadvancing strips of paper 21 and plastic 23 film approach the steel drum27 by passing under the feed guide roller 29. The paper 21 and plastic23 strips are overlapped slightly, with the plastic 23 being on the sidenext to the steel drum 27 so that the heaters 33 and 35 will come intodirect contact only with the paper 21. The heaters 33 and 35 are only aswide as the Width of overlap, and their bottom surfaces are curved tomatch the curvature of the surface of the drum 27. After the paper/filmstrip 37 has passed around the steel drum 27 and under the two heaters33 and 35, it passes under the takeoff guide roller 31 to a take up roll(not shown).

In one specific example of a paper/plastic heat sealing operation, thepaper employed was polyacrylamide coated alpha-cellulose paper 4 milsthick. The plastic film was 3mil polyvinyl chloride film that was bothheat sealable and heat shrinkable. The radius of the steel drum was655/16 inches, and the heaters were 1s-inch wide by 2 inches long(length was measured in a straight line from front edge to back edge,and not along the curved bottom or contact edge), and were made fromaluminum. The paper and plastic strips were advanced at a speed of 45feet per minute. The tirst heater 33 pressed down on the paper/ filmoverlap with a force of 5.4 pounds and was at a temperature of about 750A1C. The second heater 35 pressed on the overlap with a force of 5.8pounds and was at a temperature of about 650 C.

Because the lm that is being heat sealed to the paper is also heatshrinkable, it may be desired to provide means *for cooling during theheat sealing operation in order to eliminate the possibility of anysignificant amount of shrinkage occurring in the film at this stage ofthe operation. Means for accomplishing this purpose will be apparent tothose of ordinary skill in the art. For instance, the support surfaceopposite the hot surface may be cooled.

FIGS. 1 thru 9 show various stages in the construction of a galvaniccell in accordance with the principles of the invention. In FIG. 1, ametal battery can 39 (e.g., a magnesium or zinc can) suitable for use inthe invention is shown. (While for purposes of illustration, a round canis shown, other shaped cans such as square cans can be used in theinvention.) In FIG. 2, a liner, shown generally as 41, is shown beinginserted into the metal can 39. The liner 41 is simply the at linershown in FIG. l0, that has been rolled up into a cylinder. The paper 21portion of the liner 41 is inserted tirst, leaving the plastic lmportion 23 at the top. In FIG. 3, the linear 41 fully inserted in thecan 39 is shown. In-FIG. 3, it is seen that the height of the liner 41is the same as the inside depth of the metal can 39. However, ifdesired, the liner 41 can extend a short distance outside of the can 39.In the drawings (FIGS. 4-9) the plastic film 23 is shown on the outsideof the paper 21, that is, at the seam 25 the plastic film 23 contactsthe can 39. If desired, this can be reversed and the paper 21 can be onthe outside.

The method Afor inserting the liner 41 into the can 39 is not critical.This 'operation can be performed manually by rolling up the liner into acylinder and inserting it in the can. 'One method that has been devisedfor commercial operation is described in an application by Donald R.Trask, entitled Apparatus for Forming a Cylinder, assigned to the sameassignee as this application, and being filed concurrently herewith.

In FIG. 4, the insertion of a conventional bottom paper liner 43 into acan 39 already lined with a liner 41 of this invention is shown. Theinsertion of said bottom liner 43 is entirely conventional in the art.(In FIGS. 4-9, the thicknesses of the paper 21 and plastic film 23 areexaggerated for purposes of illustration.) In FIG. 5, the lined can isshown after the depolarizing mix 45 has been added. The addition of thedepolarizing mix 45 is conventional in the art, and can be done by themethod described in the aforementioned `U.S. Pat. No. 2,962,844, as wellas the patent to M. Orlando, U.S. Pat. No. 3,198,221.

In the next step of the construction of the cell of the invention, thecurrent collecting rod 47 is inserted in the depolarizing mix 45. Thisoperation is done by any standard procedure, such as that shown inOrlando et al., U.S. Pat. No. 2,962,844. In FIG. 6, the raw cell afterthe current collecting rod 47 has been inserted in the depolarizing mix45 is shown. After the insertion of the current collecting rod 47, theheight of the mix 45 in the can 39 is established. In general it ispreferred that the top edge of the paper 21 be at a level that isapproximately at or slightly below the level of the top surface of themix 45.

Of course, the depolarizer mix and current collecting rod could beinserted as a preformed bobbin, if desired.

In the next step in the process for producing the galvanic cells of theinvention, the portion of the plastic film 23 that extends above thesurface of the mix 45 is heat shrunk away from the inner surface of thewall of the can 39 in order to make room for the subsequent insertion ofa closure disc or other sealing means. The heat shrinking can be done byexposing the open top of the raw cell to a hot air gun 49, asis shown inFIGS. 7 and 8.

As a specific example of a heat shrinking operation, the plastic filmsin AA sized cells having liners made in accordance with the inventionwere heat shrunk. The plastic film employed was 3mil polyvinyl chloridefilm that was heat shrinkable in both directions. A Master PHT-l amelessheat torch (purchased from Master Applicance Corporation, Racine, Wis.53403) was employed to provide the heat. It had a nozzle shapedsimilarly to that shown in FIGS. 7 and 8, with an opening 1s-inch indiameter. The opening in the nozzle was positioned 12)s-inch above thetop of the can. At an air exit temperature of 980 F., and an airpressure of 2 p.s.i., 0.24 second residence time under the nozzle wassuicient to effect the desired heat shrink operation.

FIG. 9 shows the raw cell after the plastic film 23 has been shrunk awayfrom the inside wall of the can 39.

The remaining operations in the preparation of the cell are conventionalin the art. For instance, a closure disc (not shown) is added to sealoff the top of the can 37, as is shown in vOrlando et al., U.S. Pat. No.2,962,844.

The galvanic cells of the invention have wide utility as batteries forflashlights, portable radios, and other battery operated articles.

What is claimed is:

1. A galvanic cell comprising:

(a) a metal can having at least one wall having an inner surface, a top,and a bottom;

(b) depolarizing mix partially lling said can such that there is a spacebetween the top surface of said depolarizing mix and the 4top of saidcan;

(c) a current collecting rod in said depolarizing mix,

in contact therewith, and extending outwardly therefrom through saidspace to at least the top of said can;

(d) a paper liner having a top edge, said paper liner separating saiddepolarizing mix from said can; and

(e) a strip of plastic film attached to the entire top edge of saidpaper liner, said plastic film being shrunk away from the inner surfaceof said well.

2. The galvanic cell of claim 1 wherein said metal can is magnesium.

3. The galvanic cell of claim 1 wherein said metal can 1s zinc.

4. The galvanic cell of claim 1 wherein said plastic lm is polyethylene.

`S. The galvanic cell of claim 1 wherein said plastic lm is polyvinylchloride.

6. The galvanic cell of claim 1 wherein said top edge of said paperliner is at a level slightly below the said top surface of saiddepolarizing mix.

7. The gal-vanic cell of claim 1 wherein said top edge 0f said paperliner is at a level about the same as said top surface of saiddepolarizing mix.

References Cited UNITED STATES PATENTS 1,331,762 2/1920 Hazelett 136-1312,942,057 6/ 1960 Huber et al 136-145 2,962,844 12/1960 `Orlando et al13 6-175 X 3,573,106 3/1971 Johnson et al. 136-131 3,597,276 8/1971Jammet l36132 ANTHONY SKAPARS, Primary Examiner U.S. Cl. X.R. 136-131

